FLUSH Directive

OpenMP* Fortran Compiler Directive: Identifies synchronization points at which the implementation must provide a consistent view of memory.

Syntax

c$OMP FLUSH [(list)]

c
Is one of the following: C (or c), !, or * (see Syntax Rules for Compiler Directives).

list
Is the name of one or more variables to be flushed. Names must be separated by commas.

Description

The FLUSH directive must appear at the precise point in the code at which the synchronization is required. To avoid flushing all variables, specify a list.

Thread-visible variables are written back to memory at the point at which this directive appears. Modifications to thread-visible variables are visible to all threads after this point. Subsequent reads of thread-visible variables fetch the latest copy of the data.

Thread-visible variables include the following data items:

• Globally visible variables (common blocks and modules)
• Local variables that do not have the SAVE attribute but have had their address taken and saved or have had their address passed to another subprogram
• Local variables that do not have the SAVE attribute that are declared shared in a parallel region within the subprogram
• Dummy arguments
• All pointer dereferences

The FLUSH directive is implied for the following directives (unless the NOWAIT keyword is used):

• BARRIER
• CRITICAL and END CRITICAL
• END DO
• END PARALLEL
• END SECTIONS
• END SINGLE
• ORDERED and END ORDERED
• PARALLEL and END PARALLEL
• PARALLEL DO and END PARALLEL DO
• PARALLEL SECTIONS and END PARALLEL SECTIONS

See Also

OpenMP Fortran Compiler Directives

Example

The following example uses the FLUSH directive for point-to-point synchronization between pairs of threads:

  c$OMP PARALLEL DEFAULT(PRIVATE) SHARED(ISYNC)
        IAM = OMP_GET_THREAD_NUM( )
        ISYNC(IAM) = 0
  c$OMP BARRIER
        CALL WORK( )
  C I AM DONE WITH MY WORK, SYNCHRONIZE WITH MY NEIGHBOR
        ISYNC(IAM) = 1
  c$OMP FLUSH(ISYNC)
  C WAIT TILL NEIGHBOR IS DONE
        DO WHILE (ISYNC(NEIGH) .EQ. 0)
  c$OMP FLUSH(ISYNC)
        END DO
  c$OMP END PARALLEL